Aircraft typically include air data systems which are used to determine the longitudinal air speed, and the altitude of the aircraft. Frequently these systems are also used to measure angle of attack, and angle of sideslip. The pitot system includes one or more pitot tubes which project out, of the airframe, into the air stream, and allow the impact pressure of the atmosphere to enter the tube(s). The pitot tube has an opening, generally circular, facing forward. The opening is exposed to rain air pressure while the aircraft is moving through the air. Sensors sense a pressure differential which can be between the impact air pressure from the pitot tube and static air pressure from a static port. The air speed indicative output is provided, typically by an air data computer, to an air speed indicator in the cockpit.
The static system typically includes one or more of the static pressure ports which sense the atmospheric pressure outside of the aircraft, ideally without being influenced by pressure variances caused by movement of the aircraft. Static pressure is an important parameter that is utilized in aircraft for numerous purposes including the determination of altitude, altitude rate, airspeed and airspeed rate, which last-mentioned parameters are, in turn, used as inputs to various other devices such as flight management systems, autopilots, ground proximity warning systems and wind shear detectors. The standard atmospheric pressure sensed by the static ports is used to generate altitude indicative signals which are provided, typically by the air data computer, to an altimeter in the cockpit of the aircraft. Frequently, in newer aircraft, the static ports are integral to the pitot tubes.
Air data probes may also include pressure ports designed to measure angle of attack or angle of sideslip. Sensors sense a pressure differential between pressure ports located on the top and the bottom side of the probe to measure angle of attack. Sideslip can be measured similarly by sensing a pressure differential between ports located on the left and right sides of the probe or can alternately be measured by comparing pressures from a left side probe with that from a right side probe.
The pitot tube(s), static ports, and other associated ports, of an air data system can sometimes develop blockages which seriously affect the accuracy of the sensed pressures, and therefore seriously affect the accuracy of the determined air speed, altitude, or other measured air data parameters. The pitot tubes and static ports can be blocked with foreign materials caused by insects, bird strikes, volcanic ash, icing and other debris for example. Pitot ports are especially vulnerable to blockage because the pitot opening is forward facing and is therefore the most susceptible to icing or ingestion of foreign material.
There is currently no reliable system and method for detecting whether a pitot tube and/or static port is either malfunctioning or is indeed blocked by any of the aforesaid debris. For instance, in regards to a blocked pitot tube and drain hole, current technology relies on sensing a constant (trapped) pressure by comparing with other sources or systems which is unreliable (e.g., a blockage may have no impact on the measured pressures if it occurs while the aircraft is at a constant airspeed & altitude). Thus, multiple common mode failures may make it difficult or impossible to determine which, if any, systems are still operating correctly. Further, current technology cannot distinguish between a blocked port and a problem associated with the pressure sensor and may also incorrectly vote out a properly functioning pressure measurement if two or more channels are in error by approximately the same amount.